Tunnel MR head with closed-edge laminated free layer

ABSTRACT

In a tunnel magnetoresistive (TMR) device, free sublayers are separated by an intermediate spacer layer that serves to ensure a uniform circumferential magnetization in the free stack, counterbalancing orange-peel coupling by antiferromagnetic exchange coupling. Thus, a CPP MR device may have a seed stack, a pinned stack on the seed stack, and a tunnel barrier on the pinned stack. A free stack can be on the tunnel barrier, and the free stack can include structure for promoting uniform circumferential magnetization in the free stack.

I. FIELD OF THE INVENTION

The present invention generally relates tocurrent-perpendicular-to-plane (CPP) magnetoresistive devices, such astunnel magnetoresistive (TMR) devices for, e.g., disk drive read heads.

II. BACKGROUND OF THE INVENTION

In magnetic disk drives, data is written and read by magnetictransducers called “heads.” The magnetic disks are rotated at highspeeds, producing a thin layer of air called an air bearing surface(ABS). The read and write heads are supported over the rotating disk bythe ABS, where they either induce or detect flux on the magnetic disk,thereby either writing or reading data. Layered thin film structures aretypically used in the manufacture of read and write heads. In writeheads, thin film structures provide high areal density, which is theamount of data stored per unit of disk surface area, and in read headsthey provide high resolution.

The present invention is directed generally to devices that can be used,in some implementations, as heads for disk drives, and more particularlythe present invention is directed to CPP devices such as tunnelmagnetoresisitive (TMR) devices. A TMR device has at least two metallicferromagnetic layers separated by a very thin nonmagnetic insulatingtunnel barrier layer, wherein the tunneling current perpendicularlythrough the layers depends on the relative orientation of themagnetizations in the two ferromagnetic layers. The highmagnetoresistance at room temperature and generally low magneticswitching fields of the TMR renders it effective for use in magneticsensors, such as a read head in a magnetic recording disk drive, andnonvolatile memory elements or cells for magnetic random access memory(MRAM).

In a TMR device, one of the ferromagnetic layers has its magnetizationfixed, such as by being pinned by exchange coupling with an adjacentantiferromagnetic layer, and the field of the other ferromagnetic layeris “free” to rotate in the presence of an applied magnetic field in therange of interest of the read head or memory cell.

Hard bias material typically is deposited on the sides of the sensorstack, between the stack and the outer magnetic shield, to stabilize thefree layer. As understood herein, however, use of this hard biasmaterial can reduce sensor sensitivity because the non-magnetic spacingbetween the hard bias and free layer necessitates an increase of thehard bias field for achieving proper free layer stability. The resultingmagnetic field from the hard bias increases the effective anisotropy ofthe sensor, thus reducing its amplitude. Another artifact of side hardbias is the increase in the off-track reading sensitivity due the factthat side signals can enter the sensor through the hard bias materialsince the magnetic shield is relatively distanced from the sides of thesensor stack by the hard bias material.

The TMR sensor also must conform to size limitations. The resistance ofthe TMR sensor is inversely proportional to the area of the sensor,which is a product of the sensor track width and stripe height. Increasein the areal density of magnetic recording necessitates smaller sensortrack width, which in TMR devices leads to prohibitively high sensorresistances. As recognized herein, however, if the stripe height can beincreased while maintaining magnetic stability, narrow track widthwithout increased sensor resistance can be achieved.

Accordingly, as critically recognized herein, it is desired to eliminatehard bias material on the sides of the sensor stack while nonethelessmaintaining the stability of the free layers and while minimizing theresistance across the sensor to advantageously permit longer stripeheights (i.e., the distance from the air bearing surface of the sensorto the back edge of the sensor). While in-stack hard bias layers havebeen proposed, the present invention recognizes that such designs do notadequately ensure free layer stability. With these observations in mind,the invention herein is provided.

SUMMARY OF THE INVENTION

The present invention may be implemented in a CPP device such as a TMRdevice to provide one or more of the following advantages: aself-stabilizing free layer without the need of hard bias material onthe sides of the sensor stack, with cancellation of edge charges; use ofa relatively long stripe height without reducing stability andsensitivity to thereby promote low track width with acceptable sensorresistance; and a relatively soft free layer with a uniform effectiveH_(k).

Accordingly, a tunnel magnetoresistive device has a pinned ferromagneticlayer with its magnetization direction substantially prevented fromrotation in the presence of an applied magnetic field. The device alsoincludes an insulating tunnel barrier layer on the pinned layer and afree ferromagnetic stack on the tunnel barrier layer with itsmagnetization direction substantially free to rotate in the presence ofan applied magnetic field. The free ferromagnetic stack has an upperfree sublayer, a lower free sublayer, and a spacer layer disposedbetween the free sublayers. The free sublayers are in contact with eachother through opposed shoulders. The spacer layer does not extendcompletely to the ends of the lower free sublayer.

The shoulders have the same magnetic moment as that of the freesublayers. They may be made of the same material as the free sublayers,in which case the shoulders define a thickness that is the same as athickness defined by each of the free sublayers.

The pinned and free stacks define opposed sides, and no hard biasmaterial is disposed on sides of the stacks. Indeed, an insulator may beon the sides of the stack and a magnetic shield may cover the insulatorin contact therewith without intervening hard bias material.

In another aspect, a CPP MR device includes a seed stack, a pinned stackon the seed stack, and a tunnel barrier on the pinned stack. A freestack is on the tunnel barrier. The free stack includes means forpromoting uniform circumferential magnetization in the free stack.

In still another aspect, a method for making a CPP MR device includesforming a lower free sublayer on a tunnel barrier, and forming a spacerlayer on the lower free sublayer. The method also includes forming anupper free sublayer on the spacer layer. A protective mask is thenformed over the upper free sublayer, with unmasked portions of the upperfree sublayer and spacer layer removed but substantially none of thelower free sublayer being removed. The method then includes forming, onthe lower free sublayer next to ends of the upper free sublayer andspacer layer, shoulders having a magnetic moment matched to a magneticmoment of the lower and upper free sublayers.

The details of the present invention, both as to its structure andoperation, can best be understood in reference to the accompanyingdrawings, in which like reference numerals refer to like parts, and inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a hard disk drive, showing onenon-limiting environment for the present invention;

FIG. 2 is a cross-sectional view of an embodiment of a non-limiting TMRdevice made in accordance with the present invention, after the primaryTMR stack has been established and before further processing;

FIG. 3 shows the TMR device of FIG. 2, after depositing the photoresistmask, with portions of the device below the tunnel barrier omitted forclarity of exposition;

FIG. 4 shows the TMR device of FIG. 3 after reactive ion etch of certainportions, with portions of the device below the tunnel barrier omittedfor clarity of exposition;

FIG. 5 shows the TMR device of FIG. 4 after ion beam deposition of theshoulders, with portions of the device below the tunnel barrier omittedfor clarity of exposition;

FIG. 6 shows the TMR device of FIG. 5 after deposition of the alumina,with portions of the device below the tunnel barrier omitted for clarityof exposition;

FIG. 7 shows the TMR device of FIG. 6 after etching away portions of thealumina, with portions of the device below the tunnel barrier omittedfor clarity of exposition;

FIG. 8 shows the TMR device of FIG. 7 after milling away exposedportions of the stack, with portions of the device below the tunnelbarrier omitted for clarity of exposition;

FIG. 9 shows the TMR device of FIG. 8 after depositing the side layersof alumina and the side shields, with portions of the device below thetunnel barrier omitted for clarity of exposition;

FIG. 10 shows the TMR device of FIG. 9 after removing the photoresistmask by chemical-mechanical polishing, with portions of the device belowthe tunnel barrier omitted for clarity of exposition; and

FIG. 11 shows the TMR device of FIG. 10 after depositing the S2 seedlayer and side plating, with portions of the device below the tunnelbarrier once again illustrated for completeness.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, a magnetic disk drive 30 includes aspindle 32 that supports and rotates a magnetic disk 34. The spindle 32is rotated by a spindle motor that is controlled by a motor controllerwhich may be implemented in the electronics of the drive. A slider 42has a combined read and write magnetic head 40 and is supported by asuspension 44 and actuator arm 46 that is rotatably positioned by anactuator 47. The head 40 may be a GMR or MR head or othermagnetoresistive head. It is to be understood that a plurality of disks,sliders and suspensions may be employed. The suspension 44 and actuatorarm 46 are moved by the actuator 47 to position the slider 42 so thatthe magnetic head 40 is in a transducing relationship with a surface ofthe magnetic disk 34. When the disk 34 is rotated by the spindle motor36 the slider is supported on a thin cushion of air known as the airbearing that exists between the surface of the disk 34 and an airbearing surface (ABS) of the head. The magnetic head 40 may then beemployed for writing information to multiple circular tracks on thesurface of the disk 34, as well as for reading information therefrom. Tothis end, processing circuitry 50 exchanges signals, representing suchinformation, with the head 40, provides spindle motor drive signals forrotating the magnetic disk 34, and provides control signals to theactuator for moving the slider to various tracks. The componentsdescribed above may be mounted on a housing 55.

Now referring to FIG. 2, the head 40 which is manufactured using theprocess of the present invention includes a TMR stack that may be formedon a substrate such as but not limited to a lower shield layer S1. Innon-limiting implementations a pinned stack 60 may be formed on a seedlayer 61 such as a bi-layer seed layer made of Ta/Ru or NiFeCr or Cuthat is on the substrate and that in turn is covered by anantiferromagnetic sublayer 62 which may be made of IrMn, PtMn, IrMnCr,without limitation.

In the non-limiting embodiment shown, the pinned stack 60 can include afirst pinned ferromagnetic sublayer 64 that may be made of, e.g., CoFe.The sublayer 64 is formed on the antiferromagnetic sublayer 62 as shown.Above the first pinned ferromagnetic sublayer 64 is a template sublayer66 and on top of that a second pinned ferromagnetic sublayer 68, withthe template sublayer 66 being made of, e.g., Ru or Cr or Ir and withthe second pinned ferromagnetic sublayer 68 being made of CoFe or CoFeB,in non-limiting embodiments. The ferromagnetic sublayers 64, 68 arecalled “pinned” because their magnetization direction is prevented fromrotation in the presence of applied magnetic fields in the desired rangeof interest for the TMR device. Without limitation, the sublayers 64,66, 68 respectively may be, e.g., forty Angstroms thick/4.5 Angstromsthick/forty Angstroms thick.

Other CoFe and NiFe alloys may be used for the ferromagnetic sublayersand other antiferromagnetic materials may include NiMn and IrMn. Thesubstrate may be a silicon wafer if, for instance, the device is amemory cell, and ordinarily would be the bottom electrically conductivelead located on either the alumina gap material or the magnetic shieldmaterial on the trailing surface of the head carrier if the device is aread head.

Formed on the pinned stack 60 is a tunnel barrier layer 70 that is madeof an insulating tunnel barrier material. By way of non-limitingexample, the barrier layer 70 may be five to fifteen Angstroms thick andmay and may be made by depositing Aluminum on the pinned stack 60 andthen oxidizing it to create an Al₂O₃ insulating tunnel barrier layer 70.While Al₂O₃ may be used, a wide range of other materials may be used,including MgO, AlN, aluminum oxynitride, oxides and nitrides of galliumand indium, and bilayers and trilayers of such materials.

A lower free ferromagnetic sublayer 72 is on the tunnel barrier 70 asshown. The lower free sublayer 72 may be made of, e.g., NiFe or CoFe. By“free” is meant that the magnetization direction of the free stack 72 isnot pinned by exchange coupling, and is thus free to rotate in thepresence of applied magnetic fields in the range of interest.

A free spacer layer 74 that may be Tantalum or Copper or Ruthenium orTungsten can be provided on the lower free sublayer 72. On top of thespacer layer 74, an upper free sublayer 76 made of, e.g., NiFe or CoFeor CoFeB is deposited. A cap 78 made of, e.g., Tantalum is deposited onthe upper free sublayer 76.

FIGS. 3-11 illustrate a non-limiting method for processing the stackshown in FIG. 2. First, as shown in FIG. 3 a stack or mask 80 ofphotoresist and duramide is deposited over the area of the TMR stackthat will eventually form the head. Next, as shown in FIG. 4, an ionmill process may be used to remove areas of the TMR stack that areoutside the mask 80, down to the free sublayer 72.

Proceeding to FIG. 5, ion beam deposition may be used to depositshoulders 82 onto the top of the unprotected portion of the freesublayer 72, on top of the mask 80, and onto the exposed sides of theprotected areas of the TMR stack. The shoulders 82 may be made of NiFeor CoFe, and may be made of the same material as the free sublayer 72 ormay be made of a different material, provided that the magnetic momentsof the shoulders 82 and all free sublayers are matched. When theshoulders 82 are made of the same material as the free sublayers, themagnetic matching can be achieved by making the thickness of theshoulders the same as the thickness of each free sublayer. In the eventthat the shoulders are made of a different material than the freesublayer or sublayers, the magnetic matching can be achieved byappropriately establishing the thickness of the shoulders relative tothe thickness of each free sublayer.

FIG. 6 shows that a layer 84 of alumina is next deposited over theshoulders 82, preferably at a thickness that is the same as thethickness of the free sublayer 72.

FIG. 7 shows that the portions of the layer 84 of alumina that overliethe mask 80 and the top surface of the shoulders 84 are removed by,e.g., reactive ion etch, leaving the alumina substantially only on thesides of the mask 80. All areas of the TMR stack that are notsubstantially under the mask 80 with alumina layer 84 on its sides arethen removed by, e.g., a milling process, as shown in FIG. 8. It is tobe understood that the TMR stack may assume a slightly trapezoidal shapein the section shown in FIG. 8, flaring slightly outwardly as shown fromthe free sublayer 72 down.

Turning now to FIG. 9, a second layer 86 of alumina is deposited ontothe sides of the first layer 84 and the exposed sides of the TMR stackas shown. Also, the second layer 86 of alumina is surrounded by a shield88 which may be made of, e.g., NiFe. Chemical-mechanical polishing (CMP)is then used to remove the mask 80, as illustrated in FIG. 10.

As also shown, substantially all portions of the alumina layers 84, 86and shield 88 that are above the Tantalum cap are removed by the CMP,with the top of the cap lying just below the top surface of theshoulders 82, which is flush with the top surfaces of the remainingportions of the first and second alumina layers 84, 86 and shield 88 asshown.

FIG. 11 shows that an S2 seed layer 90 is then plated or otherwiseformed on the structure shown in FIG. 10.

In effect, stable circumferential magnetization is established in thecombined structure that includes the shoulders 82 and the freesublayers, which are effectively stabilized. Improved sensor sensitivityis achieved owing to the omission of hard bias material on the sides ofthe sensor stack, with a relatively softer free stack being providedwhich has a uniform effective H_(k). The anisotropy of the free stacksublayers is set in the longitudinal direction such that the combinationof the shoulders and free stack sublayers counterbalances orange peelcoupling.

While the particular TUNNEL MR HEAD WITH CLOSED-EDGE LAMINATED FREELAYER as herein shown and described in detail is fully capable ofattaining the above-described objects of the invention, it is to beunderstood that it is the presently preferred embodiment of the presentinvention and is thus representative of the subject matter which isbroadly contemplated by the present invention, that the scope of thepresent invention fully encompasses other embodiments which may becomeobvious to those skilled in the art, and that the scope of the presentinvention is accordingly to be limited by nothing other than theappended claims, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more”. For instance, the invention can apply to CPPdevices other than TMR devices, e.g., CPP GMR devices. It is notnecessary for a device or method to address each and every problemsought to be solved by the present invention, for it to be encompassedby the present claims. Furthermore, no element, component, or methodstep in the present disclosure is intended to be dedicated to the publicregardless of whether the element, component, or method step isexplicitly recited in the claims. Absent express definitions herein,claim terms are to be given all ordinary and accustomed meanings thatare not irreconcilable with the present specification and file history.

1. A tunnel magnetoresistive (TMR) device comprising: a pinnedferromagnetic layer having a magnetization substantially prevented fromrotation in the presence of an applied magnetic field; an insulatingtunnel barrier layer on the pinned layer; and a free ferromagnetic stackon the tunnel barrier layer and having at least one magnetizationsubstantially free to rotate in the presence of an applied magneticfield, the free ferromagnetic stack having an upper free sublayer, alower free sublayer, and a spacer layer disposed between the freesublayers, the free sublayers being in contact with each other throughopposed shoulders, the spacer layer not extending completely to the endsof the lower free sublayer.
 2. The device of claim 1, wherein theshoulders have the same magnetic moment as that of the free sublayers.3. The TMR device of claim 1, wherein the shoulders are made of the samematerial as the free sublayers, the shoulders defining a thickness thatis the same as a thickness defined by each of the free sublayers.
 4. TheTMR device of claim 1, wherein the pinned and free stacks define opposedsides, and no hard bias material is disposed on sides of the stacks. 5.The TMR device of claim 4, comprising an insulator on the sides of thestack and a magnetic shield covering the insulator in contact therewith.6. A CPP MR device, comprising: a seed stack; a pinned stack on the seedstack; a tunnel barrier on the pinned stack; and a free stack on thetunnel barrier, the free stack including means for promoting uniformcircumferential magnetization in the free stack.
 7. The device of claim6, wherein the means for promoting includes a spacer extending only partway across the free stack between two free sublayers of the free stack,the lower free sublayer extending completely across the free stack. 8.The CPP MR device of claim 6, wherein the device is a TMR device.
 9. Thedevice of claim 6, wherein the shoulders have the same magnetic momentas that of the free sublayers.
 10. The device of claim 9, wherein theshoulders are made of the same material as the free sublayer, theshoulders defining a thickness that is the same as a thickness definedby a free sublayer.
 11. The device of claim 6, wherein the pinned andfree stacks define opposed sides, and no hard bias material is disposedon sides of the stacks.
 12. The device of claim 11, comprising aninsulator on the sides of the stack and a magnetic shield covering theinsulator in contact therewith.
 13. A method for making a CPP MR device,comprising: forming a lower free sublayer on a tunnel barrier; forming aspacer layer on the lower free sublayer; forming an upper free sublayeron the spacer layer; forming a protective mask over the upper freesublayer; removing unmasked portions of the upper free sublayer andspacer layer but removing substantially none of the lower free sublayer;and forming, on the lower free sublayer next to ends of the upper freesublayer and spacer layer, shoulders having a magnetic moment matched toa magnetic moment of the lower and upper free sublayers.
 14. The methodof claim 13, wherein the free sublayers are made of NiFe and theshoulders are made of NiFe.
 15. The method of claim 13, wherein the freesublayers are made of CoFe and the shoulders are made of CoFe.
 16. Themethod of claim 13, wherein the shoulders are made of a soft magneticmaterial and the free sublayers are a soft magnetic material that isdifferent from the material of the shoulders.
 17. The method of claim13, wherein the lower free sublayer defines opposed sides, and no hardbias material is disposed on the sides.
 18. The method of claim 17,comprising disposing an insulator on the sides and disposing a magneticshield on the insulator in contact therewith.